In conventional mechanical steering systems, a steering wheel is connected via a steering column and a steering rack to one or more vehicle wheels. When the driver applies a rotational motion to the steering wheel, the motion is transferred via the steering column to a pinion. The pinion converts the rotational motion into translational motion of a steering rack, which moves the vehicle wheels. Hence, the steering wheel, the steering rack and the vehicle wheels are mechanically coupled such that the rotation of the steering wheel determines the rotation of the vehicle wheels, and vice versa.
The rotation of the steering wheel for conventional steering systems depends on a torque applied by the driver to the steering wheels. This torque controls a steering angle, a rate of change of the steering angle, and an acceleration of the rotation. Similarly, the rotation of the vehicle wheels depends on a torque applied to the vehicle wheels by an actuator, e.g., a motor arranged in the steering rack to control the rotation of the vehicle wheels. To that end, the torque applied to the vehicle wheels directly depends on the torque applied by the driver.
In conventional active steering systems, an additional actuator, such as a variable gear ratio including a harmonic motor, provides an additional degree of freedom so that the rotation of the vehicle wheels is not directly determined by the rotation of the steering wheel, but can be adjusted based on the speed of the vehicle. In conventional active steering systems, this allows to map the steering wheel torque to the vehicle wheels' torque in dependence of the speed of the vehicle. For example, at lower speeds, the active steering reduces the amount that the steering wheel must be turned, and, thus, effects performance in situations such as parking and other urban area traffic maneuvers. At higher speeds, the performance is such that the normal increased responsiveness from speed is avoided to improve directional stability.
In conventional steer-by-wire systems, there is no mechanical linkage between the steering column and the steering rack. The steering wheel and vehicle wheels coupled to two actuators. One actuator arranged in the steering column controls the rotation of the steering wheel and another actuator arranged in the steering rack controls the rotation of the vehicle wheels. Despite the elimination of the mechanical connection between the steering column and the steering rack, the conventional steer-by-wire systems maintain the relationship between the torque applied by the driver, a tactile feedback to the driver in response to applying the torque, and the torque applied to the vehicle wheels. For example, U.S. Pat. No. 6,363,305, describe a conventional method for generating an appropriate feedback torque on the steering wheel.
During a semi-autonomous driving of the vehicle, a semi-autonomous driving planning (SADP) system can assist the driver while the driver still operates the vehicle. For example, the semi-autonomous driving of the vehicle can be used for collision avoidance, stability recovery, lane keeping, see, U.S. Pat. No. 8,190,330.
Therefore, a need exists in the art for control systems for controlling a movement of a vehicle that overcome the limitations of conventional active steering systems and conventional steer-by-wire systems.